function checkForm(form) {
    if (!form.firstname.value || !form.lastname.value || !form.email.value || !form.question.value || !form.captcha.value) {
        alert('Please, fill all markered fields.');
        return false;
    }
    if (!IsValidEmail(form.email.value)) {
        alert('Please, correct email address.');
        return false;
    }
    return true;
}